Transfers which are applied to T-shirts and other articles of clothing have become very popular in the last decade. Boutiques which specialize in printing fanciful indicia, such as slogans, college names, or sports team names on T-shirts and other clothing, are commonly seen in shopping malls. The transfers at these boutiques are typically pre-printed on a substrate and are applied by operators at these boutiques to articles of clothing purchased by the consumer with a heat transfer press.
The pre-printed transfers which are applied to clothing are printed on a substrate. The substrate comprises a specialized type of paper which is of conventional design and well-known to those skilled in the art. The transfers consist of indicia from simple one-color block letters to elaborate multi-color illustrations. The transfers also come in various sizes. The transfers are printed in a mirror-image and face down on the substrate, such that when applied to a T-shirt or other article, they become intelligible to those looking at it.
To apply a prepared transfer to an article of clothing, a heated iron or press is typically used. The T-shirt is placed with the portion to be printed face up. The substrate containing the transfer is placed on the T-shirt such that the transfer is in contact with the T-shirt. Heat is then applied to the face of the substrate opposite the transfer, allowing the ink on the substrate to partially melt, and thereby releasing the transfer from the substrate and melting it onto the T-shirt. The T-shirt with the transfer attached is allowed to cool, and is then worn with the transfer attached.
In common use in the industry in making transfers is a multi-station, turret type, transfer printing press. The transfer printing press of this type has a plurality of flat beds or platens spaced along its perimeter. Corresponding to each of these beds is a series of stations whereat a part of the transfer is alternately printed and cured on the substrate. The number of stations employed depends on the number of colors to be printed on the transfer. In the past, the number of operators of the press was also determined by the number of colors to be printed on the transfer. Generally, the more colors to be printed, the more operators are necessary, however, the present press can be operated by two people. Transfers can consist of ten-colors or more.
At the initial station of the typical transfer printing press, the transfer is printed on the substrate on the flat bed or platen. The bed is typically made of metal such as aluminum or stainless steel. A screen embodying the indicia to be printed is pre-made using any conventional means well-known in the art. The indicia or design is formed in the screen by a conventional process. The screen has interstices in the places where ink of a particular color is to be deposited onto the substrate. For each color a different stencilled screen is used.
To print the transfer onto the substrate, the substrate is placed flat on the bed by the operator or an automatic paper feed. The bed typically has a means for creating a vacuum attached to it, and has holes in its top surface to draw air inward through the holes to keep the substrate on the bed by action of the vacuum on the undersurface of the substrate. Once printed with the first color, the substrate must not shift reference or it will be out of registration with the other stations which print the remaining colors.
The stencil screen embodying the indicia is placed over the substrate. Ink of one color is then flooded onto the screen and printed on the substrate by conventional means. The ink is of the type well-known in the industry for making transfers. After the ink is flooded onto the substrate, the ink is squeegeed through the screen onto the substrate leaving ink of the desired color on the substrate where the interstices in the screen appeared. The squeegee is of any type well-known in the art.
After the ink is squeegeed through the screen onto the substrate and the screen is lifted, the turret type machine is rotated to allow the vacuum bed to index to the next station where the ink is then gelled onto the substrate. The ink is cured or gelled on the substrate by any means such as heating it to a critical temperature. Heat is commonly applied by heat curing source directed toward the bed and substrate, though it may be by any known means. The temperature during the curing process must be kept within a window suitable for the ink-curing conditions, typically between 90.degree. to 125.degree. F. The bed, as it is made of metal, tends to act as a heat sink, retaining heat from the successive curing steps. If the temperature of the bed or substrate is allowed to go too high, the substrate has a tendency to scorch or burn, thereby ruining the transfer, and increasing waste and production costs. Furthermore, if the temperature is allowed to go too high, the ink will over-gel, also ruining the transfer. If the temperature is too low, the ink will not cure properly, and will not adhere to the substrate and may adhere to the screen at the next print station. The transfer must be flexible to conform to the shape of the article on which it is to be printed. The transfer must also be cured and dried uniformly. If it is not, there will be irregularities in the transfer, and it will have a tendency to peel off of the substrate at the irregularities.
The above process is repeated for every color to be contained in the transfer. The substrate is pre-shrunk as it comes from the manufacturer, i.e., all moisture is removed from it. The substrate has a tendency to expand when subjected to atmospheric conditions, especially when subjected to humidity. Thus, it is important that each color of the transfer must be applied to a substrate before it changes dimensions.
Furthermore, heat buildup may occur on the bed and substrate, thus interfering with the inking and drying process. The substrate would also have a tendency to burn quicker as a result of the heat buildup. If the heat buildup is too severe, it may require stopping the printing process to allow the bed and substrate to cool. This requires additional time which significantly slows down the production process.
A need has developed for an improved transfer printing press which will allow for removal of the heat applied to the substrate so that it may be controlled, thereby reducing the likelihood of burning the substrate while drying or altering the dimensional characteristics from one printing station to the next. Another need has developed for a transfer printing press which will be operable by a reduced number of persons. A further need has developed for a printing press which will reduce the time the substrate is exposed to the atmosphere before the complete transfer is printed on it, keeping dimensional integrity throughout the printing process, and thereby reducing production time and costs and increasing registration quality. The transfer printing press of the present invention solves these and other problems.